A mobile communication receiver generally has an automatic gain control function of increasing or decreasing the gain of an amplifier in response to the average power level of a reception signal and keeping the input level to a demodulator constant. However, a reception signal containing an interfering wave contains a plurality of modulation signals and the ratio between the maximum peak power and the average peak power, namely, the peak factor varies according to each modulation system. Thus, it cannot be said that sufficient gain control can be performed simply by controlling the gain of the amplifier in response to the average power level of the reception signal. Then, for example, Patent Document 1 describes an art of performing optimum gain control considering not only the average power of the reception signal, but also the peak factor of the modulation signal contained in the reception signal.
FIG. 9 shows the configuration of a receiver having the automatic gain control function described in Patent Document 1. In FIG. 9, a receiver 1 amplifies a received input signal to a predetermined level by a signal amplification section 2. Output of the signal amplification section 2 is converted into a digital signal by an A/D converter 4 in a signal demodulation section 3 and the digital signal is output to a peak power calculator 5 and a channel demodulator 6.
The peak power calculator 5 calculates peak power. A channel average power calculator 7 calculates average power from output of the channel demodulator 6. The peak power calculated by the peak power calculator 5 is compared with a threshold value 9 by a power determiner 8. The average power calculated by the channel average power calculator 7 is compared with a threshold value 11 by a power determiner 10. The gain of a variable gain device 12 is increased or decreased in response to the determination result of the peak power and the average power, whereby the automatic gain control function responsive to the peak factor of the input signal is realized.
Patent Document 2 discloses a wireless reception device for determining the modulation system of a signal from header information of a reception signal and performing automatic gain control in response to the modulation system, thereby realizing an automatic gain control function responsive to the peak factor of a reception signal.    Patent Document 1: JP-A-2005-323123 (first page, FIG. 1)    Patent Document 2: JP-A-2007-124403 (third page)